The proposed phase I clinical trial is aimed at determining the relationship between UGT1A1 genotype and pharmacokinetics and toxicity of CPT-11. If UGT1A1 genotype is found to be a good predictor of CPT-11 induced gastrointestinal toxicity and its metabolism, then the UGT1A1 genotyping test may be used to individualize CPT-11 doses, thereby minimizing the gastrointestinal side effects and improving the therapeutic index of CPT-11.